by the performance, you will know. for example, say you lean it out a little and each time you do, it performs better. then at a certain point, it loses performance and sort of "stutters" at WOT. that will mean it's too lean.
once you have leaned it out to the max PERFORMANCE, check the temp and richen it until you feel comfortable with the temp. I like to run my engines a little hotter than most people. most will say to run your engine at 220, but i like to run mine at 230 and a little higher, depending on the weather (hotter the day, hotter i run the engine. the colder, the colder i'll run the engine).

for the low speed, lean it out to where you pinch the fuel line a few inches before the carb and it dies out after 3 seconds (the engine should rev up a little then die. if it just dies, too lean. if it takes a looooooooooong time to die, too rich).

good luck!